The role of dietary variables in the development and maintenance of obesity will be examined using self-selecton situations. Genetically obese rats, brain-lesioned rats, and rats made obese by dietary manipulations will be allowed to choose between separate sources of the three macronutrients, protein, fat and carbohydrate. Changes in dietary selection will also be examined as a function of changes in the flavor of each component. It is hoped that this comparative approach may delineate some of the underlying mechanisms of obesity and provide information with respect to dietary factors which may exacerbate or attenuate the obese state.